JDBC is a core API of Java 1.1 and later. It provides a standard
set of interfaces to SQL-compliant
databases.

Postgres provides a type 4
JDBC Driver. Type 4 indicates that the
driver is written in Pure Java, and communicates in the database's
own network protocol. Because of this, the driver is platform
independent. Once compiled, the driver can be used on any
platform.

To use the driver, the jar archive postgresql.jar needs to be
included in the CLASSPATH.

Example:

I have an application that uses the JDBC driver to access a large database containing
astronomical objects. I have the application and the jdbc driver
installed in the /usr/local/lib directory, and the java jdk
installed in /usr/local/jdk1.1.6.